The present invention relates to a rear converter lens apparatus to obtain a lens system having a focus length longer than that of a master lens device by the mounting of the master lens device, and an imaging system comprising the same.
So far, there has been a rear converter lens apparatus known in the art, which has mount portions, one each corresponding to the mount portion of a master lens device, and a camera body, so that a converter lens portion is inserted in between the master lens device and the camera body by way of such mount portions to extend the focal length of the whole of a lens system.
Such rear teleconverter lenses are preferably used by users on lens interchangeable, film or digital single-lens reflex cameras.
For instance, Patent Publications 1 and 2 set forth a rear converter lens apparatus as a typical such rear teleconverter lens wherein a converter lens portion has generally a power profile of, from a master lens device portion side, a positive lens group, a negative lens group and a positive lens group, going in favor of correction of aberrations.
With the rear converter lens apparatus of such a power profile shown in Patent Publications 1 and 2, however, the converter lens portion is likely to get close to the master lens device side by reason of the relations of the converter lens portion to the principal points, placing limitations to the type of the master lens device used. This results in poor versatility of the rear converter lens apparatus.
In view of such problems, the invention has for its object the provision of a rear converter lens apparatus that makes it easy to prevent the converter lens portion from getting too close to the master lens device side even at an increased magnification, and to maintain optical performance as well, and an imaging system comprising the same.
Patent Publication 1: JP(A)2002-267929
Patent Publication 2: JP(A)2004-226648